Separation of Isoeugenol from Methylcyclohexane as a Model Mixture of Biojet Fuel Purification: Solvent Selection and Liquid–Liquid Equilibrium

Abstract

The biorefinery concept emerged as an opportunity to reduce the negative effects of climate change and as a potential source of products for the fuel industry, where jet fuel produced by hydrodeoxygenation of bio-oil (denominated as biojet fuel) is of special interest. However, the presence of highly oxygenated species makes this kind of jet fuel unsuitable as a final product. Thus, it is necessary to remove phenolic compounds from its complex matrix, but the study of solvent extraction of phenolic compounds as an upgrading of a bio-oil matrix requires a thermodynamic framework to reduce the experimental effort. In this work, isoeugenol was selected as a model phenolic molecule from biojet fuel, while methylcyclohexane was selected as a representative cyclic alkane solvent from jet fuel. Three solvents were selected by a screening based on a conductor-like screening model for real solvents (COSMO-RS) to test their capability to extract isoeugenol from methylcyclohexane. The selected solvents were ethylene glycol, diethylene glycol, and 1,3-propanediol. The density and viscosity were measured for all pure compounds and the mixtures of isoeugenol + (methylcyclohexane or extracting solvent) at 101.3 kPa and temperatures from 293.15 to 333.15 K. The liquid−liquid equilibrium was also measured for all the systems of isoeugenol + methylcyclohexane + extracting solvent at 101.3 kPa and 313.15 K. Density and liquid−liquid equilibrium data were modeled with perturbed-chain statistical associating fluid theory (PC-SAFT). Viscosity was modeled using the PC-SAFT + entropy scaling theory. The results indicate that isoeugenol has a higher affinity with the selected extracting solvents than methylcyclohexane, since the excess volume for binary mixtures of isoeugenol + extracting solvent exhibits negative values, while isoeugenol + methylcyclohexane exhibits mainly positive values. The selectivity and distribution coefficient values obtained support the idea that selected solvents are good for extracting isoeugenol, where diethylene glycol is the best alternative. PC-SAFT accurately represents the liquid−liquid equilibrium with only binary interaction parameters between methylcyclohexane and the selected solvents. Then, this model can be used as a tool for the analysis and simulation of processes of isoeugenol separation in more complex liquid mixtures.